A New Reason to Catch More ZZZs?

Okay, so Christmas Eve may not be the time to be lecturing people about getting enough sleep -- at least, not people with little kids anxious to see what Santa brought them.

But a study in today's Journal of the American Medical Association adds to the growing body of evidence that getting adequate sleep may play a key role in keeping you healthy.

In the study, researchers at the University of Chicago Medical Center measured the calcification of the arteries (a strong but silent and symptom-free predictor of cardiovascular disease) of 495 healthy, middle-aged people, once at the start of the study and again five years later. They also estimated the number of hours participants slept, using a device that attaches to a person's wrist and measures sleep based on how much the person moves around in bed. Participants slept at home, not in a sleep-study lab as is common in sleep research.

The results were striking and, says researcher Diane Lauderdale, associate director of health studies at the Medical Center, surprising. Among those who slept less than five hours per night, 27 percent developed calcified arteries over the course of five years, while among those who slept five to seven hours calcified arteries were found in only 11 percent. Among people who slept more than seven hours, just 6 percent had calcified arteries. A single hour's added sleep, the study showed, reduced odds of developing calcification in the arteries by 33 percent.

The study was the first of its kind to measure sleep hours directly and objectively, not just accept participants' reports as to how much sleep they got. It builds on a body of research that has tied lack of sleep to loss of cognitive function (including memory, ability to learn, and the ability to perform challenging tasks) and, more recently, to cardiovascular health. So far, Lauderdale says, while these studies have made tantalizing connections, no direct link between sleep, or lack thereof, and cardiovascular disease has been established.

Nor has anyone yet figured out how sleep might affect the cardiovascular system. Lauderdale and her team have a few theories. First, they posit, it's possible that there's some underlying circumstance, yet to be identified, that independently affects sleep duration and the cardiovascular system, meaning that the sleep/CV connection might be kind of a red herring.

Second, they figure, the stress hormone cortisol might come into play: people who have their sleep restricted in lab settings have been found to have elevated cortisol levels, Lauderdale explains, noting that cortisol has been implicated in coronary artery disease.
Finally, because people's blood pressure drops when they sleep, people who get less sleep might have more hours with elevated blood pressure, contributing to higher blood pressure over 24 hours, which could of course do damage to their heart and arteries.

In any case, Lauderdale says, this single study's not definitive enough to compel her to recommend people get a certain number of hours of sleep. But, she says, "Across a number of studies, there's mounting evidence that show sleep duration may have chronic-disease-important health consequences."

How many hours of sleep do you get each night? Is that enough? Or do you wish you could get more?

Sleep. I think that was the thing I used to do before I had a child. I remember it vaguely...

Seriously, I used to sleep at least seven hours every night, but my daughter is a terrible sleeper, so it's been less than that for several years. And now I'm pregnant again and can't sleep, so I'm lucky if I get four hours a night. I hate it.

I do what you're not supposed to do -- sleep late on weekends. During the work week I'm up at 5:30 for a long commute, then crash on weekends to catch up on missed sleep. Sometimes I take naps on weekend afternoons, screwing up my total sleep/wake cycles. When I retire then I'll get my sleep cycles back sync.